Wireless power transfer load modulation enhancement

ABSTRACT

A wireless power transfer (WPT) receiver circuit includes a receive coil to couple to a transmit coil of a WPT transmitter circuit. A rectifier is coupled to the receive coil to generate a rectified voltage. The rectifier comprises a bridge rectifier circuit including a first set of switching elements. A load modulation circuit facilitates communication between the WPT receiver circuit and the WPT transmitter circuit. The load modulation circuit includes a single modulation capacitor and one or more modulation switching elements. At least one node of one of the modulation switching elements is connected to an input node of the rectifier.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority under 35 U.S.C. § 119from U.S. Provisional Patent Application 62/236,821 filed Oct. 2, 2015,which is incorporated herein by reference in its entirety.

TECHNICAL FIELD

The present description relates generally to wireless charging, and moreparticularly, to wireless power transfer load modulation enhancement.

BACKGROUND

Hand-held devices including wireless communication devices such asmobile phones, tablets, phablets, and personal digital assistant (PDA)are good candidates for using wireless power transfer (WPT) technologyfor battery charging. In WPT, energy is transferred from a power sourceto an electrical load without using an electrically conductive mediumsuch as a wire for power transmission. Instead, the power transfer cantake place wirelessly by using time-varying electric, magnetic, orelectromagnetic fields. The wireless energy transfer is from a wirelesspower transmitter connected to power source to one or more wirelesspower receivers that receive the energy through an intervening space.

Common WPT technologies include magnetic resonance coupling,electromagnetic induction, and radiative power transfer. The magneticresonance and electromagnetic induction solutions are used for shortdistances, whereas the radiative solution, also known as power beaming,is a far-field solution. The power beaming technique is mostlyconsidered for use by solar power satellites and drones that receiveelectrical power from one or more beams of electromagnetic radiationsuch as microwave or laser. In the magnetic resonance coupling, theenergy transfer is based on resonance between magnetic coils of thepower transmitter and the power receiver devices. In the electromagneticinduction technique, inductive coupling between coils of the powertransmitter and the power receiver devices is used for the wirelesspower transfer. Both of the magnetic resonance coupling andelectromagnetic induction techniques are based on high-frequencyelectromagnetic radiation in the range of a few hundred KHz to a few MHz(e.g., about 100 KHz-10 MHz), and their transmission efficiency is afunction of the product of the coil Q-factor and the couplingcoefficient between the coils.

BRIEF DESCRIPTION OF THE DRAWINGS

Certain features of the subject technology are set forth in the appendedclaims. However, for purpose of explanation, several embodiments of thesubject technology are set forth in the following figures.

FIG. 1 is a schematic diagram illustrating an example of a wirelesspower transfer (WPT) receiver including a load modulation circuitaccording to aspects of the subject technology.

FIGS. 2A-2D are schematic diagrams illustrating an example of a WPTreceiver circuit with improved load modulation circuit and correspondingevolution path circuits according to aspects of the subject technology.

FIG. 3 is a schematic diagram illustrating an example of an improved WPTreceiver with reduced oscillations according to aspects of the subjecttechnology.

FIG. 4 is a diagram illustrating examples of WPT receiver rectifiersincluding improved load modulation circuits using reduced number of chippins according to aspects of the subject technology.

FIG. 5 is flow diagram illustrating a method of enhancing loadmodulation in a WPT receiver according to aspects of the subjecttechnology.

FIG. 6 is a block diagram illustrating an example wireless communicationdevice in accordance with one or more implementations of the subjecttechnology.

DETAILED DESCRIPTION

The detailed description set forth below is intended as a description ofvarious configurations of the subject technology and is not intended torepresent the only configurations in which the subject technology may bepracticed. The appended drawings are incorporated herein and constitutea part of the detailed description. The detailed description includesspecific details for the purpose of providing a thorough understandingof the subject technology. However, the subject technology is notlimited to the specific details set forth herein and may be practicedwithout one or more of the specific details. In some instances,structures and components are shown in block diagram form in order toavoid obscuring the concepts of the subject technology.

In one or more aspects of the subject technology, a device and circuitsare provided for wireless power transfer (WPT) load modulationenhancement. The subject technology enables reducing the number ofcapacitors of the load modulation circuit and the number ofsemiconductor chip pins used by the load modulation circuit. In someaspects, the disclosed technology allows configuring the desired loadimpedance of various standards in a multi-standard receiver by changinga series resistance. In one or more aspects, external capacitors can beused to reduce power consumption during modulation. In some aspects,modulation capacitors can be replaced by on-chip or external resistorsto create a fixed or a variable modulation resistance. In some aspects,the subject solution changes the modulation strength and/or the amountof oscillation dampening and reduces power dissipation and ripples onthe rectified voltage.

FIG. 1 is a schematic diagram illustrating an example of a wirelesspower transfer (WPT) receiver 100 including a load modulation circuit120 according to aspects of the subject technology. The WPT receiver 100includes a magnetic coupling circuit 102, a rectification and regulatorcircuit 110 and the load modulation circuit 120. The magnetic couplingcircuit 102 includes a coupling inductor L and tuning capacitor C1 andC2. The coupling inductor L is a receiver coil that magnetically couplesto a transmit coil of a WPT transmitter that is positioned near the WPTreceiver 100. In one or more implementations, the magnetic couplingbetween the receive and transmit coils is a magnetic resonance couplingthat provides a highest amount of coupling at a resonance frequency(e.g., 6.78 MHz for the AirFuel wireless standard). The tuning capacitorC1 and C2 can be fixed or variable capacitors and their capacitancevalues can set the resonance frequency. The WPT transmitter circuit (notshown for simplicity) can be powered by the power line and can induce anexcitement current (e.g., a sinusoidal current) into the couplinginductor L, which results in an AC input voltage (e.g., a sinusoidalvoltage) at input nodes of the rectification and regulator circuit 110(e.g., pins 122 and 125). The amplitude of the AC input voltage can bechanged, for example, by changing the frequency of the excitationcurrent away or close to the magnetic resonance frequency.

The magnetic coupling between the transmit coil and the receive coil Ldepends, among other factors, on the physical distance of these coils.For example, if the distance is too far for the magnetic coupling toinduce a desired power level in the WPT receiver 100, a signal iscommunicated to the WPT transmitter to alert the WPT transmitter. Inresponse, the WPT transmitter can either increase the excitementcurrent, or if that is not possible, inform the WPT receiver 100 bysending a signal back to alert a user of the WPT receiver 100 to take asuitable action. The communication between the WPT transmitter and theWPT receiver 100 can take place through a communication channel. In someimplementations, the communication channel is provided via loadmodulation that in the receiver side can be implemented using the loadmodulation circuit 120.

The rectification and regulator circuit 110 includes a rectifier 130 anda regulator 140. In some implementations, the rectification andregulator circuit 110 is a chip with inputs pins 122, 123, 124, and 125and an output pin 144. The rectifier 130 is a bridge rectifier includingswitches S1, S2, S3, and S4 and can rectify the AC input voltage (e.g.,a sinusoidal voltage) provided between the pins 122 and 125 and providea rectified voltage (Vrect) at an output node 142 of the rectifier 130.In some aspects, the switches S1, S2, S3, and S4 are field-effecttransistor (FET) switches. The FET switches S1 and S3 are referred to asthe high-side FET switches and one of them is on (conducting) at anyhalf cycle of the AC input voltage. For example, when the voltage at thepin 122 is positive (e.g., at positive cycle of the AC input voltage),the FET switch S1 is on and the FET switch S3 is off (non-conducting).Similarly, one of the FET switches S2 and S4, referred to as thelow-side FET switches, is on at any half cycle of the AC input voltage.For example, when the voltage at the pin 122 is positive, the FET switchS2 is off and the FET switch S4 is on. The conducting states (e.g., onor off) of the FET switches S1, S2, S3, and S4 are controlled viavoltages applied to their respective gate terminals by a gate-drivecontrol circuit, not shown here for simplicity.

In some implementations, the regulator 140 is a switching regulator suchas a buck regulator or a low-drop-out (LDO) regulator that can convertthe rectified voltage (Vrect) to a regulated DC output voltage at anoutput pin 144. The regulator 140 includes FET switches S5, S6, and S7which are controlled by applying suitable gate voltages to gateterminals of the FET switches.

The load modulation circuit 120 includes a modulation capacitor CMcoupled between the pins 123 and 124 of the rectification and regulatorcircuit 110 (e.g., a chip), the modulation switches (e.g., FET switchessuch as power FET switches) SM1 and SM2, and a modulation controlcircuit 126. The voltages of gate terminals of the FET switches SM1 andSM2 are controlled by the modulation control circuit 126. The modulationcontrol circuit 126 can apply a modulation pulse to the gate terminal ofthe FET switch SM1 and SM2. In some aspects, the modulation controlcircuit 126 controls amplitude and pulse-width of the modulation pulseto control the modulation strength of the load modulation circuit 120.In one or more aspects, the modulation control circuit 126 can beimplemented with known circuitry including analog and/or digitalcircuits.

In some implementations, the functionalities of the modulation controlcircuit 126 can be performed by, for example, a processor such a generalprocessor or a microcontroller of a host device (e.g., a mobile phone)that includes the WPT receiver 100. In one or more aspects, themodulation scheme used by the modulation control circuit 126 is anamplitude-shift-keying (ASK) modulation scheme. The ASK modulationrepresents digital data as variations in the amplitude of a carrierwave. In an ASK system, the binary symbol 1 is represented bytransmitting a fixed-amplitude carrier wave and fixed frequency for abit duration of T seconds. If the signal value is 1 then the carriersignal will be transmitted, otherwise, a signal value of 0 will betransmitted.

It is noted that the previous solutions used two modulation capacitors(e.g., with capacitance values of about 20-60 nF at a few hundred KHzfrequency) which are replaced by the single modulation capacitor CM ofthe disclosed load modulation circuit 120, thus saving one capacitor.The single modulation capacitor CM may have half of the capacitancevalue of the two modulation capacitors. It is understood that theoperating frequency varies in the range of about 100-200 KHZ forwireless power consortium (WPC) standard and in the range of about100-400 KHZ for power matters alliance (PMA) and or AirFuel inductivestandards.

FIGS. 2A-2D are schematic diagrams illustrating an example of a WPTreceiver circuit 200A with improved load modulation circuit andcorresponding evolution path circuits 200B through 200D, according toaspects of the subject technology. The WPT receiver circuit 200Aincludes a magnetic coupling circuit 202, a load modulation circuit 220,a rectifier 230, and a regulator 240. The magnetic coupling circuit 202is similar to the magnetic coupling circuit 102 of FIG. 1, describedabove. The rectifier 230 is similar to the rectifier 130 of FIG. 1 andincludes high-side FET switches S1 and S3 and low-side FET switches S2and S4. In some implementations, the low-side FET switches S2 and S4 canbe finger FETs with multiple (e.g., two) fingers. For example, the FETswitch S2 can be implemented as two FET switches S21- and S2-2.Similarly, the FET switch S4 can be implemented as two FET switches S4-1and S4-2. The finger FET realization of the low-side FET switches S2 andS4 is beneficial in the implementation of the load modulation circuit220, as explained below. The regulator 240 can be a switching regulatorsuch as an LDO regulator or a buck regulator, as explained above.

The load modulation circuit 220 does not include any modulationcapacitor (e.g., CM of FIG. 1) and only includes modulation switch FETsS2-2 and S4-2, which are modulated by a modulation control circuit, suchas the modulation control circuit 126 of FIG. 1 described above. In someaspects, the modulation switch FETs S2-2 and S4-2 are part of therectifier low-side FET switches S2 and S4. In other words, the subjecttechnology can further enhance the load modulation circuit 120 of FIG. 1by achieving load modulation without the modulation capacitor CM and themodulation FET switches SM1 and SM2 of FIG. 1 and leveraging two fingersof the low-side FET switches S2 and S4 of the rectifier 230. This can beunderstood by the analysis of the evolution path circuits 200B through200D, described herein.

The circuit 200B of FIG. 2B shows a conventional load modulation circuitwith two modulation FET switches SM1 and SM2 and two modulationcapacitors CM1 and CM2. The effect of the modulation capacitors CM1 andCM2 is understood to be injecting current to or drawing current from theFET switches SM1 and SM2. In the circuit 200C of FIG. 2C, the modulationcapacitors CM1 and CM2 are replaced by differentiators D1 and D2 andgain stages A1 and A2. The combination of each differentiator (e.g., D1)with a respective gain stage (e.g., A1) can emulate a capacitor currentgiven by C dV/dt, where C is the capacitance and V is the voltage acrossthe capacitor C. The combination of the differentiator D1 with therespective gain stage A1 can generate the dV/dt and C terms of thecapacitor current. Thus, the circuit 200C of FIG. 2C can be thought ofas an equivalent of the circuit 200B of FIG. 2B, in which a currentpulse is injected into a resistor, such as an on-resistance of the FETswitch SM1.

In the circuit 200D of FIG. 2D, the functionality of the differentiatorsD1 and the gain stage A1 is performed by providing a current via the FETswitch S1 and pulsing the gate terminal of the SM1 for a short time(e.g., 100 ns). The circuit 200D is similar to the circuit 200A of FIG.2A, in which the FET switches S2-2 and S4-2 (e.g., fingers of the FETswitches S2 and S4) are respectively pulsed at the beginning of theconduction time of the FET switch S1 (e.g., positive half-cycle of theAC input voltage) and the conduction time of the FET switch S3 (e.g.,negative half-cycle of the AC input voltage).

FIG. 3 is a schematic diagram illustrating an example of an improved WPTreceiver 300 with reduced oscillations according to aspects of thesubject technology. The WPT receiver 300 includes a magnetic couplingcircuit 302, a load modulation circuit 320, a rectifier 330, a regulator340, and an additional load circuit 350. The magnetic coupling circuit302, the load modulation circuit 320, the rectifier 330, and theregulator 340 are similar to the magnetic coupling circuit 102, the loadmodulation circuit 120, the rectifier 130, and the regulator 140 of FIG.1 as described above. The improvement in the WPT receiver 300 is due tothe additional load circuit 350 that includes the resistor R1 (theadditional load) and a damping switch S8 that is operable to connect theresistor R1 to ground potential when closed.

The additional load R1 adds to the amount of load introduced at therectifier output node 342 by the regulator 340 to provide a minimum loadthat can significantly reduce oscillations associated with the loadmodulation circuit 320. In some aspects, reducing oscillations isachieved by closing the damping switch S8 to apply the damping load(e.g., R1) in a time window including a modulation event. As explainedabove, the modulation FET switches of the load modulation circuit 320are controlled by a modulation pulse provided by a modulation controlcircuit (e.g., 126 of FIG. 1). In one or more aspects, the modulationevent is the application of the modulation pulse to a gate terminal of amodulation FET switch of the load modulation circuit 320.

In some implementations, reducing the oscillations due to loadmodulation can be enhanced by increasing on-resistance of the modulationFET switches (e.g., SM1 and/or SM2). An additional benefit of increasingthe on-resistance (Rds) of the modulation FET switches is that allowscontrolling of the modulation strength of the load modulation circuit.

In one or more implementations, adjustable resistors (e.g., Rv1 or Rv2)can be coupled in parallel or in series with capacitor C of the loadmodulation circuit 320, which would be in series with the modulation FETswitches (e.g., FET switches SM1 and SM2). In some aspects, anadjustable resistance or current sink can be employed in the rectifierFET switches S2 and S4 and be turned on when the rectifier FET switchesS1 and S3 are in on states.

In some implementations, values of the adjustable resistors can bedetermined based on a rectified output voltage (V_(rect)) of therectifier 330 or an output voltage (e.g., at node 344) of the voltageregulator 340. In some aspects, adjusting the value of the adjustableresistors Rv1 or Rv2 can be performed during the time window includingthe modulation event. In some implementations, instead of coupling theadjustable resistors Rv1 or Rv2, a current sink, which are known circuitelements, may be coupled in series with the first set of switches.

In some aspects, when a PMOS FET or an NMOS FET with a charge pump isused for FET switches SM1 and SM2, the gate voltages of these FETS canbe higher than available positive AC (ACP) and negative AC (ACN) supplyvoltages. In some implementations, this can be overcome by reusing thecharge pump employed for the rectifier NMOS FET switches to create thehigher voltage for the modulation FET switches.

FIG. 4 is a diagram illustrating examples of WPT receiver rectifiers410, 420, 430, 440, and 450 including improved load modulation circuitsusing reduced number of chip pins according to aspects of the subjecttechnology. The subject technology not only enables implementing theload modulation circuit with one modulation capacitor (e.g., 120 ofFIG. 1) or without any modulation capacitors (e.g., 220 of FIG. 2A), butfurther facilities reducing the number of pins of the receiver chip thatare used for coupling the load modulation circuit to the receiver chip,as discussed herein.

WPT receiver rectifier 410, shown in FIG. 4, is the existing solutionand is shown here to emphasize the distinction of the subject technologyin terms of reducing the number of modulation capacitors and the numberof chip pins. The WPT receiver rectifiers 410 includes load modulationcircuits 412 (e.g., 412-1 and 412-2), and a rectifier 130. Each loadmodulation circuit (e.g., 412-1) includes two modulation capacitors CM1and CM2, modulation FET switches SM1 and SM2. The modulation FETswitches of the load modulation circuits 412 are controlled bymodulation control circuits M1 and M2. The coupling of the loadmodulation circuits 412 to the rectifier chip is seen to consume sixpins (e.g., 414 through 419).

In the WPT receiver rectifier 420 of the subject technology, for eachload modulation circuit (e.g., 422-1), the number of modulationcapacitors are reduced to one (e.g., CM1) by moving the modulation FETswitches to one side, as shown by SM12, and using a single controlcircuit (e.g., M1) to control the modulation FET switches. This hasreduced the number of pins to 4 pins (e.g., 414 through 417).

The WPT receiver rectifier 430 is another version of the WPT receiverrectifier 420, in which the number of modulation capacitors is reducedto one (e.g., CM1), but the FET switches are connected in series and areseparately controllable by the modulation control circuits M1 and M2.This is done while preserving the reduced number of pins (e.g., 4 pins414 through 417).

In the WPT receiver rectifier 440, the total number of modulationcapacitors is reduced to one (instead of two in 430), but the FET switchSM12 is realized by two parallel FET switches (e.g., fingers of a fingerFET) which are connected in parallel with the modulation FET switchSM22. The modulation FET switches receive separate control pulses from asingle modulation controller circuit M. This is done while reducing thenumber of pins to three (e.g., 414, 415, and 417).

The WPT receiver rectifier 450 is another version of the WPT receiverrectifier 440, in which the modulation FET switch SM12 is realized bythree parallel FET switches (e.g., fingers of a finger FET) which areconnected in series with the modulation FET switch SM22. The modulationFET switches receive separate control pulses from a single modulationcontroller circuit M. This is done while preserving the number of pins(e.g., 3 pins 414, 415, and 417). The realization of modulation FETswitch SM12, as shown in the WPT receiver rectifier 450, allows varyingthe load impedance (e.g., capacitance and series resistance) to satisfyrequirements of various standard types or operating conditions.

FIG. 5 is flow diagram illustrating a method 500 of enhancing loadmodulation in a WPT receiver (e.g., 300 of FIG. 3) according to aspectsof the subject technology. The method 500 starts with providing adamping load (e.g., R1 of FIG. 3)(510). The damping load is coupled toan output node (e.g., 342 of FIG. 3) of a rectifier circuit (e.g., 330of FIG. 3) of the WPT receiver using a damping switch (e.g., S8 of FIG.3) (520). Oscillations associated with a load modulation circuit (e.g.,330 of FIG. 3) of the WPT receiver are reduced by closing the dampingswitch to apply the damping load in a time window including a modulationevent (530). The load modulation circuit (e.g., 320 of FIG. 3) includesmodulation FET switches (e.g., SM1 and SM2 of FIG. 3) controlled by amodulation pulse (e.g., generated by 126 of FIG. 1). The modulationevent includes application of the modulation pulse to a gate terminal ofa modulation FET switch.

FIG. 6 is a block diagram illustrating an example wireless communicationdevice 600 in accordance with one or more implementations of the subjecttechnology. The wireless communication device 600 may comprise aradio-frequency (RF) antenna 610, a receiver 620, a transmitter 630, abaseband processing module 640, a memory 650, a processor 660, a localoscillator generator (LOGEN) 670, and a power management unit (PMU) 680.In various embodiments of the subject technology, one or more of theblocks represented in FIG. 6 may be integrated on one or moresemiconductor substrates. For example, the blocks 620-670 may berealized in a single chip or a single system on chip, or may be realizedin a multi-chip chipset.

The RF antenna 610 may be suitable for transmitting and/or receiving RFsignals (e.g., wireless signals) over a wide range of frequencies.Although a single RF antenna 610 is illustrated, the subject technologyis not so limited.

The receiver 620 may comprise suitable logic circuitry and/or code thatmay be operable to receive and process signals from the RF antenna 610.The receiver 620 may, for example, be operable to amplify and/ordown-covert received wireless signals. In various embodiments of thesubject technology, the receiver 620 may be operable to cancel noise inreceived signals and may be linear over a wide range of frequencies. Inthis manner, the receiver 620 may be suitable for receiving signals inaccordance with a variety of wireless standards. Wi-Fi, WiMAX,Bluetooth, and various cellular standards. In various embodiments of thesubject technology, the receiver 620 may not require any SAW filters andfew or no off-chip discrete components such as large capacitors andinductors.

The transmitter 630 may comprise suitable logic circuitry and/or codethat may be operable to process and transmit signals from the RF antenna610. The transmitter 630 may, for example, be operable to up-covertbaseband signals to RF signals and amplify RF signals. In variousembodiments of the subject technology, the transmitter 630 may beoperable to up-convert and amplify baseband signals processed inaccordance with a variety of wireless standards. Examples of suchstandards may include Wi-Fi, WiMAX, Bluetooth, and various cellularstandards. In various embodiments of the subject technology, thetransmitter 630 may be operable to provide signals for furtheramplification by one or more power amplifiers.

The duplexer 612 may provide isolation in the transmit band to avoidsaturation of the receiver 620 or damaging parts of the receiver 620,and to relax one or more design requirements of the receiver 620.Furthermore, the duplexer 612 may attenuate the noise in the receiveband. The duplexer may be operable in multiple frequency bands ofvarious wireless standards.

The baseband processing module 640 may comprise suitable logic,circuitry, interfaces, and/or code that may be operable to performprocessing of baseband signals. The baseband processing module 640 may,for example, analyze received signals and generate control and/orfeedback signals for configuring various components of the wirelesscommunication device 600 such as the receiver 620. The basebandprocessing module 640 may be operable to encode, decode, transcode,modulate, demodulate, encrypt, decrypt, scramble, descramble, and/orotherwise process data in accordance with one or more wirelessstandards.

The processor 660 may comprise suitable logic, circuitry, and/or codethat may enable processing data and/or controlling operations of thewireless communication device 600. In this regard, the processor 660 maybe enabled to provide control signals to various other portions of thewireless communication device 600. The processor 660 may also controltransfers of data between various portions of the wireless communicationdevice 600. Additionally, the processor 660 may enable implementation ofan operating system or otherwise execute code to manage operations ofthe wireless communication device 600. In one or more aspects thatprocessor 660 may control the operation (e.g., closing or opening ofvarious FET switches) of the circuits of the subject technology, forexample, FET switches SM1, SM2, S1-S4, and S8 of FIG. 3 or FET switchesof other figures disclosed herein. In one or more implementations, theprocessor 660 can perform the functionalities of the modulation controlcircuit 126 of FIG. 1.

The memory 650 may comprise suitable logic, circuitry, and/or code thatmay enable storage of various types of information such as receiveddata, generated data, code, and/or configuration information. The memory650 may comprise, for example, RAM, ROM, flash, and/or magnetic storage.In various embodiment of the subject technology, Information stored inthe memory 650 may be utilized for configuring the receiver 620 and/orthe baseband processing module 640.

The local oscillator generator (LOGEN) 670 may comprise suitable logic,circuitry, interfaces, and/or code that may be operable to generate oneor more oscillating signals of one or more frequencies. The LOGEN 670may be operable to generate digital and/or analog signals. In thismanner, the LOGEN 670 may be operable to generate one or more clocksignals and/or sinusoidal signals. Characteristics of the oscillatingsignals such as the frequency and duty cycle may be determined based onone or more control signals from, for example, the processor 660 and/orthe baseband processing module 640.

In operation, the processor 660 may configure the various components ofthe wireless communication device 600 based on a wireless standardaccording to which it is desired to receive signals. Wireless signalsmay be received via the RF antenna 610 and amplified and down-convertedby the receiver 620. The baseband processing module 640 may performnoise estimation and/or noise cancellation, decoding, and/ordemodulation of the baseband signals. In this manner, information in thereceived signal may be recovered and utilized appropriately. Forexample, the information may be audio and/or video to be presented to auser of the wireless communication device, data to be stored to thememory 650, and/or information affecting and/or enabling operation ofthe wireless communication device 600. The baseband processing module640 may modulate, encode and perform other processing on audio, video,and/or control signals to be transmitted by the transmitter 630 inaccordance to various wireless standards.

The PMU 680 includes a power supply that can provide power to allcircuits and modules of the wireless communication device 600. The powersupply can use a battery voltage or can generate a rectified andregulated voltage from the power line to support one or more voltagerails of the wireless communication device 600. In one or more aspects,the PMU 680 can include a WPT circuit including a WPT receiver circuitsuch as the PWT receiver circuits 100 of FIG. 1, 200A of FIG. 2A, or 300of FIG. 3 and can use the subject technology to efficiently receivepower from a WPT transmitter.

The previous description is provided to enable any person skilled in theart to practice the various aspects described herein. Variousmodifications to these aspects will be readily apparent to those skilledin the art, and the generic principles defined herein may be applied toother aspects. Thus, the claims are not intended to be limited to theaspects shown herein, but are to be accorded the full scope consistentwith the language claims, wherein reference to an element in thesingular is not intended to mean “one and only one” unless specificallyso stated, but rather “one or more.” Unless specifically statedotherwise, the term “some” refers to one or more. Pronouns in themasculine (e.g., his) include the feminine and neuter gender (e.g., herand its) and vice versa. Headings and subheadings, if any, are used forconvenience only and do not limit the subject disclosure.

The predicate words “configured to”, “operable to”, and “programmed to”do not imply any particular tangible or intangible modification of asubject, but, rather, are intended to be used interchangeably. Forexample, a processor configured to monitor and control an operation or acomponent may also mean the processor being programmed to monitor andcontrol the operation or the processor being operable to monitor andcontrol the operation. Likewise, a processor configured to execute codecan be construed as a processor programmed to execute code or operableto execute code.

A phrase such as an “aspect” does not imply that such aspect isessential to the subject technology or that such aspect applies to allconfigurations of the subject technology. A disclosure relating to anaspect may apply to all configurations, or one or more configurations. Aphrase such as an aspect may refer to one or more aspects and viceversa. A phrase such as a “configuration” does not imply that suchconfiguration is essential to the subject technology or that suchconfiguration applies to all configurations of the subject technology. Adisclosure relating to a configuration may apply to all configurations,or one or more configurations. A phrase such as a configuration mayrefer to one or more configurations and vice versa.

The word “example” is used herein to mean “serving as an example orillustration.” Any aspect or design described herein as “example” is notnecessarily to be construed as preferred or advantageous over otheraspects or designs.

All structural and functional equivalents to the elements of the variousaspects described throughout this disclosure that are known or latercome to be known to those of ordinary skill in the art are expresslyincorporated herein by reference and are intended to be encompassed bythe claims. Moreover, nothing disclosed herein is intended to bededicated to the public regardless of whether such disclosure isexplicitly recited in the claims. No claim element is to be construedunder the provisions of 35 U.S.C. § 112, sixth paragraph, unless theelement is expressly recited using the phrase “means for” or, in thecase of a method claim, the element is recited using the phrase “stepfor.” Furthermore, to the extent that the term “include,” “have,” or thelike is used in the description or the claims, such term is intended tobe inclusive in a manner similar to the term “comprise” as “comprise” isinterpreted when employed as a transitional word in a claim.

What is claimed is:
 1. A wireless power transfer (WPT) receiver circuitcomprising: a receive coil configured to couple to a transmit coil of aWPT transmitter circuit; a rectifier coupled to the receive coil andconfigured to generate a rectified voltage, wherein the rectifiercomprises a bridge rectifier circuit including a first set of switchingelements; and a load modulation circuit configured to facilitatecommunication between the WPT receiver circuit and the WPT transmittercircuit, the load modulation circuit comprising a single modulationcapacitor and one or more modulation switching elements, wherein atleast one node of one of the one or more modulation switching elementsis connected to an input node of the rectifier, wherein the one or moremodulation switching elements comprises two field-effect transistor(FET) switches, wherein the single modulation capacitor is connectedbetween first nodes of two FET switches, and wherein the WPT transmittercircuit further comprises at least one variable resistor connected inseries or in parallel with the single modulation capacitor.
 2. The WPTreceiver circuit of claim 1, wherein, second nodes of the two FETswitches are connected to the input nodes of the rectifier.
 3. The WPTreceiver circuit of claim 1, wherein the one or more modulationswitching elements comprises a FET switch coupled in series with thesingle modulation capacitor.
 4. The WPT receiver circuit of claim 3,wherein the load modulation circuit comprising the FET switch coupled inseries with the single modulation capacitor is coupled between inputnodes of the rectifier.
 5. The WPT receiver circuit of claim 4, whereinthe FET switch comprises a finger FET including multipleparallel-connected FET switches, and wherein the finger FET enableschanging an on-resistance of the FET switch by at least one of changingthe FET fingers or a gate voltage of the FET switch.
 6. The WPT receivercircuit of claim 5, wherein gate terminals of the multipleparallel-connected FET switches are independently controlled by amodulation control circuit.
 7. The WPT receiver circuit of claim 1,wherein the one or more modulation switching elements comprise a FETswitch coupled in series with the single modulation capacitor and afinger FET including multiple parallel-connected FET switches.
 8. TheWPT receiver circuit of claim 1, wherein the receiver coil is configuredto electromagnetically couple to the transmit coil.
 9. The WPT receivercircuit of claim 1, wherein the first set of switching elements of thebridge rectifier circuit comprise FET switches having respective gateterminal voltages controlled by a control circuit based on a voltage ofa node of the load modulation circuit.
 10. A wireless power transfer(WPT) receiver circuit comprising: a receive coil configured to coupleto a transmit coil of a WPT transmitter circuit; a rectifier coupled tothe receive coil and configured to generate a rectified voltage, whereinthe rectifier comprises a bridge rectifier circuit including a first anda second pair of switching devices, and wherein each switching device ofthe first pair of switching devices includes at least twoparallel-connected switching elements; and a load modulation circuitconfigured to facilitate communication between the WPT receiver circuitand the WPT transmitter circuit, the load modulation circuit comprisingmodulation switch elements wherein the modulation switch elementscomprise FET switches coupled in series to adjustable resistors and to asingle modulation capacitor.
 11. The WPT receiver circuit of claim 9,wherein first and a second pair of switching devices comprisefield-effect transistor (FET) switches, and wherein the at least twoparallel-connected switching elements comprise FET switches.
 12. The WPTreceiver circuit of claim 11, wherein the modulation switch elementscomprise two modulation FET switches, wherein each modulation FET switchis connected between an input node of the rectifier and a ground nodeconnected to a ground potential.
 13. The WPT receiver circuit of claim12, further comprising a modulation control circuit configured to applya modulation pulse to a gate terminal of each modulation FET switch, andwherein the modulation control circuit is configured to control anamplitude and a pulse-width of the modulation pulse to control amodulation strength of the load modulation circuit.
 14. The WPT receivercircuit of claim 13, wherein the second pair of switching devicesincludes a first FET switch coupled between a first input node of therectifier and a ground node connected to a ground potential and a secondFET switch coupled between a second input node of the rectifier and theground node, and wherein the first and the second FET switchesincorporate a modulation FET resistance.
 15. The WPT receiver circuit ofclaim 14, wherein the modulation control circuit is configured to applythe modulation pulse to a gate terminal of a modulation FET switch whena respective first FET switch or second FET switch connected to themodulation FET switch is conducting.
 16. A method for enhancing loadmodulation in a wireless power transfer (WPT) receiver, the methodcomprising: providing a damping load; coupling the damping load to anoutput node of a rectifier circuit of the WPT receiver using a dampingswitch; reducing oscillations associated with a load modulation circuitof the WPT receiver by closing the damping switch to apply the dampingload in a time window including a modulation event; and coupling anadjustable resistor in series with a first set of FET switches of therectifier circuit, when a second set of FET switches of the rectifiercircuit are conducting current, wherein: the load modulation circuitcomprises modulation FET switches controlled by a modulation pulse, andthe modulation event includes application of the modulation pulse to agate terminal of a modulation FET switch.
 17. The method of claim 16,further comprising increasing on-resistance of the modulation FETswitches to enhance reducing of the oscillations and to controlmodulation strength of the load modulation circuit.
 18. The method ofclaim 16, wherein each of the second set of FET switches are connectedbetween an output node and input node of the rectifier circuit.
 19. Themethod of claim 18, further comprising adjusting a value of theadjustable resistor based on a rectified output voltage (V_(rect)) ofthe rectifier circuit or an output voltage of a voltage regulatorfollowing the rectifier circuit, and wherein adjusting the value of theadjustable resistor is performed during the time window including themodulation event.
 20. The method of claim 16, further comprisingcoupling a current sink in series with a first set of FET switches ofthe rectifier circuit, when a second set of FET switches of therectifier circuit are conducting current, wherein each of the second setof FET switches are connected between an output node and input node ofthe rectifier circuit.